Issue 67

M. Selim et alii, Frattura ed Integrità Strutturale, 67 (2024) 205-216; DOI: 10.3221/IGF-ESIS.67.15

The Buckling Restrained Brace (BRB) is a structural system designed to overcome limitations in moment-resisting frames (MRFs) and concentrically braced frames (CBFs) by providing sufficient stiffness and ductility. It consists of a central steel core enclosed in a buckling-restraint mechanism, which generates and dissipates energy through stable tension-compression hysteretic cycles, preventing brace buckling [11-13]. BRB development consists of three phases: The initial external restraining system comprises a concrete-infilled steel section combined with a steel core, which can take the form of a plate, I section, or other steel cross-section [14-17]. The complexities of pouring and curing concrete pose challenges in achieving precise configuration of the steel core and the gap between the concrete and steel core. All-steel BRB offers advantages such as easy on-site assembly, reduced weight, convenient replacement of inner core members, and inspection and reuse of external restraining systems [18, 19]. Researchers have further advanced the concept in earthquake engineering, developing various BRBs to maximize their potential in the field [19, 20]. Studies are ongoing to investigate the behavioral characteristics of BRBs, and there are advancements in the development of new devices [21-26]. In Japan, BRBs have been successfully tested for seismic protection of steel buildings, although their usage is currently limited. In this context, BRBs are considered as hysteretic dampers and are incorporated into moment resisting frame MRFs that possess high stiffness and strength. Additionally, a dual system can be achieved by utilizing concentrically braced frames CBF with BRBs placed parallel to the MRF [27-29]. External restraining systems employ hollow cross-sections with either rectangular or circular shapes. To enhance the capacity of BRBs, it is necessary to increase the thickness of the element in relation to the inner core plate [30-33]. External restraining systems enable the inner core members to yield completely, leading to enhanced lateral stiffness and stable dissipation of hysteretic energy [34]. Buckling-restrained braces (BRBs) offer lateral stiffness and energy absorption during seismic events. They are commonly used in framed structures, long-span structures, and bridge structures to enhance the lateral resistance, energy dissipation capacity, and ductility [35, 36]. A new type of all-steel BRB, called pre-tensioned cable-stayed BRB (PCS-BRB), is proposed. This design adds a supplementary structural system of pre-tensioned cables and cross-arms on the exterior of a typical BRB. The external restraining system comprises of cable-stayed and outer restraining tubes, which enhance its external flexural stiffness. This design is suited for stadiums, high building, and other buildings where PCS-BRBs are exposed to high loads Guo et al [32, 37, 38]. Externally, pre-tensioned cable systems have been found to effectively increase the load-carrying capacity of slender compression members. This can be achieved by incorporating lateral cross-arms into the external casing discovered that a pre-tensioned system with a single cross-arm significantly enhances the member's overall capacity and improves the hysteretic response of BRB members. This method has demonstrated an improvement in the overall performance of BRBs [38]. This research aims to enhance rectangular BRBs with pre-tensioning systems. Finite Element Analysis (FEA) was used to investigate the impact of different configurations and initial pre-tensioning force values on traditional all-steel BRB members, in this study was performed through the following steps: - Verification study on rectangular BRB using 3D finite Element Analysis. - Using double pre-tensioning system on rectangular BRB to minimize thickness of external case. - Parametric study on different parameters (pre-tensioning force value - steel grade). he main components of the studied BRB specimen are core plate, which represents the main item of the specimen, external case laterally supported by pre-tensioning steel cables to prevent the out-of-plane buckling. Two cross arms perpendicular to the external case were provided to connect the cables to the case. The steel core plate consists of a yielding segment, steel core projections, and transition segments. The axial friction between the core and the external case was avoided through a 2.5 mm gap between them. The FEA commercial code Abaqus 2020 [39] was used to simulate the behavior of the BRB. The eight-node solid element with linear reduced integration (C3D8R) was used to simulate the 3D model elements, including core, external case, and pre-tensioning cables, as shown in Fig. 1. The core plate lateral deformations put the core plate into contact with the external case, the surface-to-surface contact was utilized to simulate that contact. The contact properties used in normal and tangential directions were hard contact property and Coulomb Mohr friction, respectively. The friction coefficient was 0.1. The Abaqus/Explicit analysis tool offers two approaches to constraint enforcement: "Hard" Contact, which uses the Lagrange multiplier technique, and "Penalty contact enforcement," T N UMERICAL SIMULATION AND VERIFICATION

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